The application relates to a photographic system, including photographic products and processes, which utilize compounds capable of releasing a photographically useful material when contacted with an aqueous alkaline processing composition.
In various photographic systems for forming images, whether in black and white or in color, it is often desirable to include in the photographic film unit one or more of the various photographic reagents required for development and/or to enhance image quality. This practice extends to both conventional systems for forming negative images and also to various systems such as diffusion transfer wherein a positive image in silver or in color is obtained. In many instances the photographic reagent may be contained initially in either the processing composition applied for development and image formation or in the film unit itself. The latter embodiment is typically preferred so as to reduce the number of ingredients required in the processing composition. In other instances the particular photographic reagent is not sufficiently stable in alkali to provide the requisite shelf life for the processing composition or the reagent is not compatible and/or reacts with another reagent in the processing composition and therefore must be contained initially in the film unit. In still other instances the reagent must be provided at some particular time in the development process which requires that it be present in a specified layer or in specified proximity to another layer in the film unit.
In all the foregoing instances it is desirable that the reagent be contained in the desired layer or layers in a form that is stable and non-migratory or nondiffusible and yet available when required at a particular time in the development process. To accomplish this result it is known in the art to attach a blocking moiety which prevents the reagent from reacting with the other photographic materials present in the film unit or migrating or diffusing prior to the time when photographic development is effected but which will release the photographic reagent at the desired time such as by reaction with the aqueous alkaline processing composition.
It is known in the art to utilize development restrainers and development restrainer precursors in photographic applications. A predetermined level of development usually will take place before the development restrainers or development restrainer precursors function to inhibit or control further development. The blocked development restrainers are designed to provide a controlled release of the development restrainer during the development process. Such blocked development restrainers are disclosed, for example, in U.S. Pat. Nos. 3,260,597 and 3,265,498 which disclose hydrolyzable blocked restrainers; U.S. Pat. No. 3,698,898 which discloses the use of guinone--or naphthoquinonemethide precursors which release a photographic reagent such as 1-phenyl-5-mercaptotetrazole in the presence of alkali; U.S. Pat. No. 3,938,996 which discloses the use of a carbocylic blocking group which includes an oxime group (e.g. --C.dbd.N--OH); U.S. Pat. No. 4,009,029 which discloses a class of cyanoethyl--containing blocked development restrainers; and German Offenlegungsschrift No. 2,427,813 which discloses various blocked development restrainers.